Systematics and Evolution Abstracts

The origins of marine adaptations in late Cretaceous pythonomorphs- an exploration of indistinct traits using an updated phylogeny of Mosasauroids

Michelle Campbell, M.Sc.

For most aquatic reptiles, features including paddle-like limbs and tails, buoyancy adaptations, and streamlining make it evident that they are aquatic. During the Cretaceous, a group of lizards, the pythonomorphs, transitioned into marine environments. They would eventually evolve into mosasaurs, top predators of the Cretaceous oceans. Yet, these earliest semi-aquatic lizards were missing these distinctive aquatic adaptations and thus must have had indistinct aquatically adapted morphologies supporting their initial success. Through the description and morphological analysis of two new Croatian fossils – a well preserved, nearly complete Pontosaurus and an incomplete, unidentified pythonomorph– and firsthand observation of previously described taxa, I will develop a phylogeny of early mosasauroids and their kin. This character-based phylogeny will be used to assess the pattern and distribution of basal marine adaptations, and to examine subsequent, increasingly aquatic, transformations of those adaptations in relation to our understanding of their paleoecology and phylogeny.This project aims to determine basal, non-distinct adaptations in aquatic lizards radiating into marine environments, which could be used to identify early marine adaptations in convergent taxa. This research will increase understanding of this enigmatic land to sea transition, and contribute to overall knowledge of marine lizard evolution.

Running with dinosaurs: allometry and cursorial trends among carnivorous theropods

Scott Persons, Ph.D.

The relative lengths of limb bones have long been recognized as correlates of running ability in terrestrial tetrapods. That relationship offers the potential to examine extinct lineages for evidence of large-scale adaptive trends in cursoriality. Among dinosaurs, however, such potential examinations are undermined by the tremendous range of body sizes and potentially confounding allometric effects on limb proportions. Based on a sample of 61 non-avian theropod specimens, each representing a distinct genus, it is confirmed that the lengths of the distal limb bones are negatively affected by allometric factors, and a method is developed to correct for these factors. This allows limb-proportion adaptations to be recognized and compared between theropods that differ by several magnitudes in body size. Results show that ontogenetic changes in limb proportions observed in many theropods do not differ from the limb proportion changes that would be predicted based strictly on the changes in body size. Evidence of an adaptive trend towards improved cursoriality is confirmed among several theropod groups. A trend towards reduced running ability is found among dromaeosaurids, which is contrary to the widespread view that dromaeosaurids were among the most cursorially adapted of all predatory dinosaurs.

To Improve Upon a Master: A Re-description of Mosasaurus

Hallie Street, Ph.D.

The first mosasaur fossils were discovered during the second half of the 18th century. It took a few decades for the implications of these discoveries to be fully understood; Mosasaurus was one of the first fossils that forced contemporary scientists to confront the concept of extinction. The second, more complete fossil was a skull described by the famous anatomist Georges Cuvier in 1808. However, at the time, the rules of zoological nomenclature had not yet been established, so no taxonomic name accompanied Cuvier’s description. The specimen was eventually named Mosasaurus hoffmannii, but the genus and species were erected separately without new descriptions, with little to no reference to Cuvier’s description, and without designating a holotype specimen. Following its discovery, many unrelated fossils were allied with Cuvier’s ‘grand animal de Maastricht’. Since then, the fossils that were clearly not mosasaurs have been removed, but the genus remains poorly defined. This study aims to report on preliminary progress of efforts to revise the genus Mosasaurus based on an expansion of Cuvier’s original description.

Whose the Boss?: A description of Pachyrhinosaurus histology

Elizabeth Kruk, M.Sc.

Pachyrhinosaurus is a ceratopsian dinosaur from the Late Cretaceous of Alberta. Typical ceratopsians have nasal and supraorbital horns, and a parietal-squamosal frill, but pachyrhinosaurs differ in that they have cranial bosses in place of horns. A boss is a large mass of bone, generally rugose in nature. The histology of the pachyrhinosaur nasal boss material can be described as secondarily trabecular, (remodeled bone) with primary interstitial fibrolamellar bone, only containing primary osteons. Fibrolamellar bone is woven with osteons -blood vessel canals- embedded within it. Furthermore, the nasal boss is intramembranous, meaning it is an elaboration of the dermatocranium. Recently, a new Pachyrhinosaurus specimen (UALVP 53300) has been discovered, which has thicker trabeculae than other specimens described so far. In the near future, I intend to section other ceratopsian cranial material to compare the histological structure, since there is minimal literature on the microstructure of the Pachyrhinosaurus bosses. This research should help to explain the size of the nasal boss and thicker traberculae on UALVP 53300.

When did ‘Frog’ Crabs started looking like Frogs? New fossil evidence from the Early Cretaceous of Tropical South America

Javier Luque, Ph.D.

The Brachyura, or ‘true’ crabs are the most derived and diverse group of crustaceans, first known from the Mid Jurassic (~160 Ma.), and rapidly diversified worldwide during the Cretaceous (~146 to 66 Ma.). Since then, crabs have exploded in form and function, leading to the incredible morphological diversity seen today. One extant group known as ‘frog’ crabs, or Raninoidans, has puzzled scientists since the days of Lamarck with their unusual elongated carapaces, narrow sterna, and paddle-like legs. However, ancient raninoidans were more typically crab-like, with ornamented roundish to hexagonal carapaces and broader sterna, obscuring the phylogenetic relationships among fossil and extant lineages. Despite this, phylogenetic analyses support the monophyly of Raninoida. Although they diversified and spread worldwide during the Albian (~112-99.6 Ma.), pre-Albian fossils are scarce and fragmentary, further biasing our understanding of raninoidan origins. Recent discoveries from Colombia and Brazil indicate that early raninoidans were much more diverse than previously thought, and that the frog-like body plan had already evolved once in pre-Aptian times (~125 Ma.). These findings challenge the current hypotheses of a high-latitude origin, and suggest that the equatorial Neotropics played an important role on the origin and evolution of ancient true crabs.

Fine-scale analysis of population structure of polar bears (Ursus maritimus) and their movements within in the Hudson Bay

Michelle Viengkone, M.Sc.

This study seeks to re-evaluate and provide additional fine-scale analysis of the population structure of Hudson Bay polar bears (Ursus maritimus) in relation to their movement. Within the region, four subpopulations are currently recognized on a genetic basis (Paetkau et al. 1999): Western Hudson Bay; Southern Hudson Bay; Davis Strait; and Foxe Basin. We will re-evaluate this structure by genotyping 420 bears from throughout the region using 24 known hypervariable ursid microsatellite loci and a further 9000 SNP markers to achieve maximal power to detect differentiation. In addition, through an analysis of movement data, it will be possible to assess the potential basis of structure by using radio collar data of females during the breeding season. Using this structure data, a pedigree can be constructed to inform relatedness and relationships amongst the subpopulations. With this information it is possible to achieve a better understanding about the gene flow amongst subpopulations and their genetic compositions, which will aid in future management efforts.

Molecular analysis of putative hybridization in the Papilio machaon species group (Lepidoptera: Papilionidae) in North America

Julian Dupuis, Ph.D.

Evidence of hybrid speciation in animals is becoming increasingly common in recent years. As study systems, butterflies have played a disproportionately large part in developing our understanding of the evolutionary processes at work. Papilio brevicauda and P. joanae are species of swallowtail butterflies endemic to the Maritime Provinces and the Ozark mountains, respectively. Morphologically they resemble P. polyxenes, but preliminary analysis of mitochondrial DNA clusters them with P. machaon, suggesting possible hybrid ancestry. Here, we use ten microsatellite loci, nuclear and mitochondrial sequence data, and morphometric analysis of wing patterns to clarify the ancestry of these flagship species. Although maternally inherited mitochondrial markers do cluster P. brevicauda and P. joanae with P. machaon, population admixture analyses using microsatellites show closer relationships with P. polyxenes. Morphometric ordinations of wing characters also cluster the putative hybrids more closely to P. polyxenes, although overall, hybrid clusters are intermediate between the putative parental species. These results support an ancient hybrid origin for P. brevicauda and P. joanae. Consequently, this system provides a valuable snapshot of downstream artifacts produced by homoploid hybridization (~10,000 years after initial hybridization), thus complimenting the understanding we have gained by documenting recent hybridization events.

A population genomics approach to the designation of conservation units

Sim Zijian, M.Sc.

The thinhorn sheep (Ovis dalli) is a charismatic mountain ungulate discontinuously distributed from northwestern Alaska to northern British Columbia. O. dalli is a popular game species and its management relies heavily upon the delineation of biologically relevant conservation units from which game management zones are derived. The rise of high throughput next generation sequencing offers an exciting opportunity to adopt a population genomics approach in the designation of conservation units informed by both neutral and adaptive genetic variation. An explicit assessment of neutral variation allows for a better understanding of demographic history and processes such as population bottlenecks and gene flow, which can be used to identify genetically discrete population groups. Understanding the patterns of adaptive differentiation can help in the preservation of evolutionary potential crucial for long-term viability of the species in light of a changing climate and pressures from selective harvesting. Utilizing a genome wide array of SNPs, this study will quantify the spatial pattern of neutral and adaptive genetic diversity of thinhorn sheep inhabiting BC and the Yukon. Results will be used to guide the establishment of appropriate management zones and the prioritization of conservations efforts to achieve optimal use of limited resources.

Arctic Grayling Diversity in a Disturbed Landscape

Jessica Reilly, M.Sc.

Arctic grayling (Thymallus arcticus) are cold-water, salt-water intolerant salmonids with a holarctic distribution including most of northern Canada. In Alberta, the abundance of Arctic grayling has been steadily declining since the 1950s and the species is now provincially classified as a Species of Special Concern. Although the suspected factors behind the Arctic grayling decline (e.g., overharvest, reduced habitat quality) have been documented, no genetic studies of Alberta Arctic grayling have been completed. To investigate population structure and genetic diversity, tissue has been collected from approximately 750 Arctic grayling from 24 rivers in the Hay River, Peace River and Athabasca River watersheds. We will develop and use microsatellite markers to investigate broad and fine scale population structure. It is expected that populations will be distinct between watersheds, and that structure within subwatersheds will represent a spatially nested hierarchy of sub-populations linked by infrequent gene flow. Subpopulations are likely because of varying degrees of isolation resulting from barriers, distance between subpopulations, and spawning site fidelity. We also expect genetic diversity in Arctic grayling populations to decrease in a south-eastern direction because these populations are the furthest from putative, northern refugia. In the future, we plan to use these data to investigate correlations between contemporary landscape features and genetic diversity of Arctic grayling subpopulations.

The Kids Are Alright: an analysis of independence in juvenile theropod dinosaur Gorgosaurus libratus

Gavin Bradley, M.Sc.

The social behaviour of large theropod dinosaurs such as Tyrannosaurus rex, has traditionally received little study by palaeontologists, who have instead focused on predominantly herbivorous taxa for whom pack behaviour is better represented in the fossil record. Rather than rely on the interpretation of serendipitous finds of theropod bonebeds, I plan to examine the potential for gregarious behaviour in these large carnivores by evaluating the independence of a juvenile specimen of Gorgosaurus libratus. In preparing and describing the specimen, collected at Dinosaur Provincial Park (Alberta), I will note any features associated with social behaviour, such as teeth marks from intraspecific fighting or exaggerated cranial structures that may have been related to sexual selection. The juvenile’s ability to hunt independently will then be elucidated by carrying out Finite Element Analysis to measure potential bite force, and examining histological sections of its teeth to measure the rate of mature tooth development. Additionally, Nitrogen and Carbon stable isotope values of the teeth will be calculated, revealing any variation in diet in comparison to adults of the same species. This multi disciplinary approach should give a cumulative picture of juvenile Gorgosaurus’ lifestyle and illuminate the more expansive problem of social behaviour in theropods.

The Multiple Developmental Processes of Ankylosaur Armour

Michael E Burns, Ph.D.

The Ankylosauria are a clade of ornithischian dinosaurs best known for their extensive systems of dermal armour composed of individual elements, called osteoderms. Although not uncommon among tetrapods, the morphological diversity of these elements reaches its peak in ankylosaurs. Osteoderms of the cervical region are morphologically distinct relative to other postcranial osteoderms in all ankylosaurs, but they form a unique structure in ankylosaurids. The osteoderms overlie a basal band of bone that has a smoother texture than the external osteoderms. Here I hypothesize different developmental processes to account for this and test it via the histology of cervical half rings across several disparate ankylosaur taxa. Those of basal ankylosaurs show thick, organized collagen bundles in their primary structure, a characteristic retained in derived nodosaurids. This indicates metaplastic mineralization of the dermis. The same is true for the cervical osteoderms of derived ankylosaurids. The basal bony band, however, lacks metaplastic tissue, instead showing primary fibrolamellar bone indicative of intramembranous ossification, a process reported only scarcely in amniote osteoderms. This mirrors the development of cranial ornamentation in ankylosaurids. Although interesting, the implications of the anatomical specificity of these processes (restricted to the region immediately posterior to the skull) remain unclear.